286 HYALONEMA (PRIONEMA) PINULIFUSUM. 



The lateral rays are straight, in the same spicule equal or somewhat unequal, 

 and either nearly cylindrical throughout and terminally rounded, or cylindrical 

 in their proximal part, conical in their distal part, and blunt-pointed. They 

 generally bear a small number of rather larger spines on their distal part. The 

 lateral rays are, at the base, considerably thinner than the basal part of the 

 distal ray, and attain a length of 34-52 n, on an average 44.5 m. 



The proximal ray of the hexactine forms is about as long as the laterals. 



The viedium pinules (Plate 70, figs. 20-24) are pentactine. Their distal 

 ray is straight, 165-216 ^ long, generally 167-205 ix, on an average 189 /u, and 

 5.5-9 M thick at the base. Their basal part is for a considerable distance free 

 from spines, and they end in a very short likewise spineless terminal cone. 

 Their remaining parts bear somewhat sparse and rather divergent spines which 

 are slightly curved, concave to the ray. The spines are conical, sharp-pointed, 

 about 3 M thick at the base, and attain 30 ix in length. They are usually simple; 

 occasionally one or two bear a small secondary spinelet. The maximum thick- 

 ness of the distal ray, together with the spines, is 33-48 ix. The lateral rays are 

 conical, terminally rounded, and 35-48 m long. Their distal part bears a small 

 number of rather large spines which sometimes form an irregular verticil below 

 the end of the ray. 



The small canalar pinules (Plate 70, figs. 11-14) are generally pentactine, 

 very rarely hexactine. The distal ray is 110-240 m long, generally 120-206 //, on 

 an average 167 n, and 3.5-8.3 n thick at the base. Its basal part and its long 

 and slender terminal cone are smooth; its middle-part bears a small number, 

 generally about a dozen or so, of sparse, small, straight or slightly curved spines 

 which are directed obliquely upwardly. The maximum thickness of the distal 

 ray, together with the spines, is 9-25 /u- The lateral rays are cylindrical and 

 smooth in their basal, conical and spiny in their distal part. They measure 

 28-62 II in length. The proximal ray (of the hexactine forms) is about as long 

 as the laterals. 



The superficial (hypodermal and hypogastral) pentactines have straight, 

 conical, terminally rounded rays. The dimensions of the few I was able to 

 measure are: — basal thickness of rays 10-23 m, length of proximal ray 300-410 n, 

 length of lateral rays 177-430 /i. 



The hexactine megascleres observed were 0.6-1 mm. in diameter, and had 

 straight conical rays, 10-24 ix thick at the base. 



Most of the rhabd megascleres are rather long blunt amphioxes with hardly 

 a trace of a central tyle. Besides these spicules, which form the bulk of the 



